1. Technical Field
The present invention relates to a method of identifying characteristics of an optical disk in a compact disk drive such as a compact disk read-only-memory (CD-ROM) drive, and more particularly, to a method and apparatus for efficiently determining a size of optical disk loaded in a compact disk drive in order to timely prepare subsequent operations of a compact disk drive.
2. Background Art
Generally, an optical disk player such as a CD-ROM disk player and a compact disk player requires a mechanism that automatically loads an optical disk for recording and reproducing information to and from the optical disk. Within the optical disk player, the initial playing position of an optical pick-up device relative to the optical disk will differ depending upon the type of the optical disk used. Consequently, it is necessary to first determine the type of the optical disk inserted into the optical disk player before a servo gain of a spindle motor and its driver is adjusted as is disclosed, for example, in U.S. Pat. No. 5,054,014 for Optical Disk Recording/Reproducing Apparatus And Rotary Drive Therefor issued to Ito et al., in order to perform the recording and reproduction operations. Usually, the optical disks for use in a compatible optical disk player such as a CD-ROM drive come in various diameter sizes, for example, eight centimeters and twelve centimeters. Thus, it is necessary to determine whether the optical disk inserted into the optical disk player is one of a eight centimeters disk or a twelve centimeters disk in order to proceed with the recording and reproduction operations.
Conventionally, there are a number of known techniques for determining the size of the loaded optical disk. For example, a first technique such as disclosed, for example, in U.S. Pat. No. 5,042,025 for Rotation Control System For Disk Player issued to Aoyagi et al., involves the use of photosensors arranged at a predetermined position in an optical disk player. The diameter of a loaded optical disk is determined in accordance with the presence or absence of light reflected by the optical disk. In another technique, mechanical contacts such as a carrier as is disclosed in U.S. Pat. No. 4,797,867 for Disk Detecting Apparatus issued to Hirano, are arranged at a predetermined position in an optical disk player from which the type of optical disk is determined in accordance with several successive position of the carrier. These techniques however require additional circuitry and sensors, thereby increasing the production cost.
In U.S. Pat. No. 4,653,040 for Disk Size Detecting Circuit issued to Senso, the type of disk is determined according to the angle through which a spindle motor rotates until the speed of the spindle motor reaches a predetermined value. For example, in Senso '040, a rotational speed detecting circuit employs a rotational speed pulse generator, a frequency-to-voltage converter and a comparator, is used to generate a speed signal indicating a rotational speed of the spindle motor. A frequency detecting circuit having a counter, a frequency-to-voltage converter and a comparator, is additionally used to produce an angle signal indicating an angle through which the spindle motor has rotated. The angle signal is then compared with a reference value at a transition of the speed signal when the rotational speed of the spindle motor exceeds a predetermined rotational speed in order to discriminate the size of the optical disk loaded in the optical disk player. While the disk size detecting circuit of Senso '040 has its own merit, it is my observation that the circuit requires high production cost.
Alternatively, U.S. Pat. No. 5,172,354 for Compatible Disk Player For Playing Multi-Size Disks And Having A Mode For Selecting One Disk Type issued to Otsubo, notes a disk size determining technique in which an optical pick-up device is required to move to two different playing positions to determine whether a loaded optical disk is one of a compact disk and a video disk of different diameter sizes. If such a disk size determining technique is implemented into a CD-ROM drive system however, I have discovered that the optical pick-up device must first move to predetermined locations of respective optical disks of eight centimeters and twelve centimeters, and then move to a read-in area of each optical disk where a table of contents (TOC) is recorded in order to record or reproduce information data to and from the optical disk. I have also found that this required step, consumes valuable time in the preparation of the recording and reproduction of information data to and from an optical disk.